1. Field of the Invention
The present invention relates to the structure of an optical element for preventing the outflow of an adhesive to the optically functional surface of the optical element (or plastic molding) when the optical element (or plastic molding) is adhered in a lens-barrel.
2. Description of the Related Art
Conventionally, when an optical element (or plastic molding) is fixed in a lens-barrel using an adhesive, the adhesive was filled in a concave groove (adhesive pool) formed inside the lens-barrel after fitting the optical element (or plastic molding), and the optical element (or plastic molding) was adhered and fixed in the lens-barrel with this adhesive.
The sectional view of FIG. 1 shows a structure when an optical element (or plastic molding) is assembled in a lens-barrel according to a conventional method.
This conventional example assembles two optical elements (or plastic moldings), i.e., a first optical element (or plastic molding) 100 and a second optical element (or plastic molding) 101 in a lens-barrel 20, and an optical element with the lens-barrel having two optical elements (or plastic moldings) 100 and 101 assembled in the lens-barrel 20 is mounted to the mounting holder 30 of mechanical parts to focus light beams on the imaging surface of the mechanical part.
In this conventional example, an optical-element-holding portion 21 is formed on an end of the lens-barrel 20, first the second optical element (or plastic molding) 101 is fitted in the lens-barrel 20, and placed on the optical-element-holding portion 21, then the first optical element (or plastic molding) 100 is placed on the second optical element (or plastic molding) 101. More specifically, the first optical element (or plastic molding) 100 is fitted to the lens-barrel 20 so as to depress the second optical element (or plastic molding) 101, and by adhering the first optical element (or plastic molding) 100 to the lens-barrel 20 using an adhesive A or the like, the first and second optical element (or plastic molding) 100 and 101 are fixed in the lens-barrel 20.
On the other inner periphery of lens-barrel 20, a concave groove (adhesive pool) 22 to fill the adhesive A for adhering the outer peripheral surface of the first optical element (or plastic molding) 100 is formed, and after fitting the outer peripheral surface of the first optical element (or plastic molding) 100 in the lens-barrel, the adhesive A is filled in the concave groove (adhesive pool) 22 to fix the first optical element (or plastic molding) 100 in the lens-barrel 20.
The optical element (or plastic molding) 100 is formed of an optically functional surface 1 and a flange 2′ formed on the outer periphery thereof, and the optically functional surface 1 is formed to have a high surface precision. The optical element (or plastic molding) 100 is designed so as to be fixed to the lens-barrel at the flange 2′ formed on the outer periphery of the optically functional surface 1, and as FIG. 2(a) shows, a fitting portion to the lens-barrel 20 and an adhering portion to the adhesive A are formed on the outer peripheral surface of the flange (optical element), and the optical element (or plastic molding) is supported at the fitting portion and adhered at the adhering portion.
However, when the first optical element (or plastic molding) 100 is adhered by filling the adhesive A in the concave groove (adhesive pool) 22 formed on the inner periphery of the lens-barrel, as in a conventional method, since width of the concave groove (adhesive pool) formed by cutting the inner periphery of the lens-barrel is limited by the wall thickness of the lens-barrel 20, it is difficult to insert the adhesive-supply nozzle when filling the adhesive, and when a large quantity of the adhesive is filled in the concave groove (adhesive pool) 22 having a small capacity to fill the adhesive (adhesive capacity), the adhesive A flows to the optically functional surface 1 as FIG. 2(b) shows to lower the precision of the optical element, or the adhesive A overflows to interfere with the mechanical part (mounting holder 30).
In other words, in order that the adhesive A does not flow to the flange surface and to the optically functional surface 1, the filling height of the adhesive A must be lower than the flange surface, and therefore, the adhesion area of the adhesive A is small, and the adhesion of the optical element (or plastic molding) 100 is insufficient.
On the other hand, if the concave groove (adhesive pool) 22 formed on the inner peripheral surface of the lens-barrel in order to increase the adhesive capacity and to enlarge the adhesion area, there is the possibility that the fitting area of the optical element (or plastic molding) 100 and the lens-barrel 20 is reduced, and the support of the optical element (or plastic molding) 100 by the lens-barrel 20 becomes unstable.